This application is based on Japanese Patent Application Nos. 11-282602 filed Oct. 4, 1999 and 11-312629 filed Nov. 2, 1999, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a braking pressure control apparatus including a pressurizing device in a braking system.
2. Discussion of Related Art
Japanese Patent Application No. 11-123604 which was filed by the assignee of the present application and which has not been published discloses an example of such a braking pressure control apparatus equipped with a pressurizing device. The braking pressure control apparatus disclosed in this application includes (1) a pressurizing device operable to pressurize a working fluid and control the pressure of the pressurized fluid to a desired value, (2) a plurality of pressure control valve devices each of which is disposed between the pressurizing device and at least one of a plurality of brake cylinders in the braking system and is operable to control flows of the fluid between the pressurizing device and the corresponding at least one brake cylinder, for thereby regulating the fluid pressure in each of the corresponding at least one brake cylinder, and (3) a pressurizing-device control device for controlling the pressurizing device to control the pressure of the fluid pressurized by the pressurizing device according to an operating state of a brake operating member. In the braking pressure control apparatus disclosed in the above-identified application, the pressure of the fluid delivered from the pressurizing device is controlled according to the operating state of the brake operating member, and each pressure control valve device is controlled to control the fluid pressure in each of the corresponding at least one brake cylinder in an anti-lock pressure control fashion, for example, such that the slipping state of each of a plurality of vehicle wheels corresponding to the respective brake cylinders is kept optimum.
According to the braking pressure control apparatus disclosed in the above-identified application, the pressurizing device is controlled according to the operating state of the brake operating member, irrespective of the operating states of the individual pressure control valve devices. However, it was found that the pressure of the pressurized fluid delivered from the pressuring device is influenced by the flows of the fluid through each pressure control valve device.
It is therefore an object of the present invention to provide a braking pressure control apparatus wherein the pressure of the pressurized fluid delivered from the pressurizing device is less likely to be influenced by the fluid flows through the pressure control valve devices.
The above object may be achieved according to any one of the following modes or forms of the present invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate and clarify possible combinations of elements or technical features. It is to be understood that the present invention is not limited to the technical features or any combinations thereof which will be described for illustrative purpose only. It is to be further understood that a plurality of elements or features included in any one of the following modes of the invention are not necessarily provided all together, and that the invention may be embodied without some of the elements or features described with respect to the same mode.
(1) A braking pressure control apparatus for a braking system having a plurality of brake cylinders, comprising:
a pressurizing device capable of pressurizing a working fluid and controlling a pressure of the pressurized fluid;
a plurality of pressure control valve devices each of which is disposed between the pressurizing device and at least one of the plurality of brake cylinders and is operable to control flows of the fluid between the pressurizing device and the corresponding at least one brake cylinder, for thereby regulating the fluid pressure in the corresponding at least one brake cylinder; and
a pressurizing-device control device operable to control the pressurizing device for controlling an output pressure of the pressurizing device, on the basis of an operating state of each pressure control valve device, which operating state determines a state of flow of the fluid between said pressurizing device and the corresponding at least one brake cylinder.
In the braking pressure control apparatus constructed according to the above mode (1) of this invention, the pressurizing-device control device is adapted to control the pressurizing device for controlling the output pressure of the pressurizing device, on the basis of the state of flow of the fluid through each of the pressure control valve devices between the pressurizing device and the corresponding at least one brake cylinder, so that the undesirable influence of the fluid flow between the pressurizing device and the wheel brake cylinder or cylinders on the output pressure of the pressurizing device can be reduced.
Where each pressure control valve device has a fluid-supply state for supplying the pressurized fluid from the pressurizing device to the corresponding brake cylinder or cylinders, and a closed state for inhibiting the supply of the pressurizing fluid from the pressurizing device to the brake cylinder or cylinders, for instance, the pressurizing-device control device may be arranged to control the pressuring device in different manners in the open and closed states of the pressure control valve device, respectively, or in one of different manners which is selected according to a switching operation of the pressure control valve device between the fluid-supply and closed states.
Where each pressure control valve device has a fluid-discharge state for discharging the pressurized fluid from the brake cylinder or cylinders back to the pressurizing device, and a closed state for inhibiting the discharge flow of the pressurized fluid from the brake cylinder or cylinders to the pressurizing device, for instance, the pressurizing-device control device may be arranged to control the pressurizing device in different manners in the fluid-discharge state and the closed state, respectively, or in one of different manners which is selected according to a switching operation of the pressure control valve device between the fluid-discharge and closed states.
Where each pressure control valve device is capable of changing the amounts of the fluid that are supplied to and discharged from each brake cylinder, the pressurizing-device control device may control the pressurizing device in different manners depending upon the amounts of supply and discharge of the fluid to and from each brake cylinder.
The fluid flow through each pressure control valve device has a particularly large influence on the output pressure of the pressurizing device when the pressurizing device is placed in a constant or substantially constant operating state. When the operating state of the pressurizing device is held constant, the output pressure of the pressurizing device is usually held substantially constant. If the pressure control valve device is switched from the closed state to the fluid-supply state while the output pressure of the pressurizing device is held substantially constant, the output pressure is reduced. By controlling the pressurizing device so as to increase its output pressure upon switching of the pressure control valve device from the closed state to the fluid-supply state, therefore, the reduction of the output pressure due to the switching of the pressure control valve device to the fluid-supply state can be reduced. By controlling the pressurizing device so as to reduce its output pressure upon switching of the pressure control valve device from the closed state to the fluid-discharge state, the increase of the output pressure due to the switching of the pressure control valve device to the fluid-discharge state can be reduced.
Each pressure control valve device serves to regulate the fluid pressure in only one brake cylinder, or the fluid pressure in two or more brake cylinders. The pressure control valve devices indicated above need not be provided for all of the brake cylinders.
(2) A braking pressure control apparatus according to the above mode (1), wherein the pressurizing-device control device includes a valve-device-state detecting portion operable to detect the operating state of each pressure control valve device, said pressurizing-device control device controlling the pressurizing device on the basis of the operating state detected by the valve-device-state detecting portion.
The state of fluid flow between the pressurizing device and the at least one brake cylinder is determined by the operating state of the corresponding pressure control valve device. Accordingly, the pressurizing-device control device controls the pressurizing device on the basis of the detected operating state of the pressure control valve device, in order to reduce the influence of the fluid flows on the output pressure of the pressurizing device.
Where each pressure control valve device includes a plurality of control valves, for instance, the valve-device-state detecting portion may directly detect the operating state of each of the control valves, or indirectly detect the operating state on the basis of a control command generated by a valve control device which is principally constituted by a computer and operable to control the control valves. For example, each pressure control valve device has a fluid-supply state in which the pressurized fluid is supplied from the pressurizing device to the at least one brake cylinder, and a fluid-discharge state in which the pressurized fluid delivered from the pressurizing device is not supplied to the at least one brake cylinder while the pressurized fluid is discharged from the at least one brake cylinder. The fluid-supply state is selected when the fluid pressure in the at least one brake cylinder should be increased, and the fluid-discharge state is selected when the fluid pressure in the at least one brake cylinder should be reduced. Thus, the operating state of the pressure control valve device is switched to the fluid-supply state or fluid-discharge state, depending upon whether the fluid pressure in the corresponding brake cylinder or cylinders should be increased or reduced. The presently selected operating state of the pressure control valve device is represented by the control command generated by the valve control device, and can therefore be detected on the basis of the control command. The pressurized fluid discharged from the brake cylinder in the fluid-discharge state may or may not be returned to the pressurizing device.
The valve-device-state detecting portion may be arranged to detect the operating states of all of the pressure control valve devices, or the operating states of the selected one or ones of the pressure control valve devices. Where the pressurizing device is controlled on the basis of the operating states all of the pressure control valve devices, the valve-device-state detecting portion is desirably arranged to detect the operating states of all the pressure control valve devices. Where the pressurizing device is controlled on the basis of the operating state or states of the selected pressure control valve device or devices, the valve-device-state detecting portion may be arranged to detect the operating state of only the selected at least one pressure control valve device. Where the brake cylinders are wheel brake cylinders for braking respective wheels of an automotive vehicle, the pressurizing device may be controlled on the basis of the operating states of the pressure control valve devices for the wheel brake cylinders for the front wheels, and not on the basis of the operating states of the pressure control valve devices for the wheel brake cylinders for the rear wheels. In this case, the valve-device-state detecting portion need not detect the operating states of the pressure control valve devices for the rear wheel brake cylinders. In this respect, it is noted that the front wheel brake cylinders usually have a larger braking capacity than the rear wheel brake cylinders, and the fluid flows to and from the front wheel brake cylinders have a larger influence on the output pressure of the pressurizing device. In this sense, it is reasonable to control the pressurizing device on the basis of the operating states of the pressure control valve devices for the front wheel brake cylinders.
(3) A braking pressure control apparatus according to the above mode (1) or (2), further comprising a valve-device control portion operable to control each of the pressure control valve devices on the basis of a running condition of an automotive vehicle on which the braking system is provided.
The valve-device control portion may include at least one of (a) an anti-lock pressure control portion for controlling the fluid pressure of the brake cylinder for braking a slipping wheel of the vehicle such that the slipping amount of the slipping wheel is held within an optimum range; (b) a front-rear braking-force distribution control portion for controlling the fluid pressures of the brake cylinders for braking the front and rear wheels of the vehicle such that a ratio of the total front braking force generated by the front wheel brake cylinders to the total rear braking force generated by the rear wheel brake cylinders coincides with an optimum value determined by an ideal distribution curve; (c) a braking effect control portion for controlling the fluid pressures of the wheel brake cylinders, so as to provide a total vehicle braking force as desired by the operator of the vehicle; (d)) a left-right braking-force distribution control portion for controlling the fluid pressures of the brake cylinders for braking the left and right wheels of the vehicle during turning of the vehicle, such that the total left braking force generated by the left wheel brake cylinders and the total right braking force generated by the right wheel brake cylinders are controlled so as to permit the vehicle to run with high stability; (e) a traction control portion for activating the brake cylinders for the drive wheels of the vehicle such that the slipping amounts of the slipping drive wheels are held within an optimum range; (f) a vehicle running stability control portion for controlling the wheel brake cylinders of the vehicle so as to assure stable running of the vehicle; (g) a vehicle turning stability control portion for controlling the wheel brake cylinders of the vehicle so as to assure stable turning of the vehicle; and (h) an automatic braking control portion for controlling the wheel brake cylinders of the vehicle so as to apply an automatic brake to the vehicle as needed.
(4) A braking pressure control apparatus according to any one of the above modes (1)-(3), further comprising a valve-device control portion operable for controlling each pressure control valve device such that pressure of the fluid in the corresponding at least one brake cylinder is controlled to be lower than the output pressure of the pressurizing device.
Generally, the presently established operating state of a pressure control valve device does not assure a particular fluid flow through the pressure control valve device while the pressure control valve device is held in that operating state. Where the pressure control valve device is placed in the fluid-supply state for supplying the pressurizing fluid from the pressurizing device to the brake cylinder or cylinders, the pressurized fluid is supplied to the brake cylinder or cylinders while the output pressure of the pressurizing device is higher than the fluid pressure in the brake cylinder or cylinders. After the brake cylinder pressure has been increased to the level equal to the output pressure of the pressurizing device, the pressurized fluid is no longer supplied to the brake cylinder or cylinders. The pressure control valve device may be placed in the fluid-supply device when a brake operating member is in operation, for example. In this case, the pressurized fluid may not be supplied to the brake cylinder or cylinders even while the brake operating member is kept operated. In the braking pressure control apparatus constructed according to the above mode (4), however, the valve-device control portion does not hold the pressure control valve device in the fluid-supply state until the fluid pressure in the corresponding at least one brake cylinder has been increased to the level of the output pressure of the pressurizing device, so that the pressurized fluid delivered from the pressurizing device is supplied to the corresponding at least one brake cylinder as long as the pressure control valve device is held in the fluid-supply state.
Where the pressure control valve device includes a solenoid-operated shut-off valve disposed between the pressurizing device and the corresponding at least one brake cylinder, the pressurized fluid is supplied or is not supplied to the brake cylinder or cylinders while the shut-off valve is in the open state, and is inhibited from being supplied to the brake cylinder or cylinders while the shut-off valve is in the closed state. Where the solenoid-operated shut-off valve is alternately opened and closed with a controlled duty ratio or cycle by the valve-device control portion in the apparatus according to the above mode (4), however, it is considered that the pressurized fluid is supplied to the brake cylinder or cylinders throughout the duty-ratio-controlled operation of the shut-off valve, since the brake cylinder pressure is controlled to be lower than the output pressure of the pressurizing device.
(5) A braking pressure control apparatus according to any one of the above modes (1)-(4), wherein the pressurizing-device control device includes a pressure sensor for detecting the output pressure of the pressurizing device, at a position between the pressurizing device and the corresponding at least one pressure control valve device, said pressurizing-device control device controlling the pressurizing device on the basis of the output pressure as detected by the pressure sensor.
In the braking pressure control apparatus according to the above mode (5), a change of the output pressure of the pressurizing device due to the fluid flows between the pressurizing device and the brake cylinder or cylinders through each pressure control valve device is detected directly by the pressure sensor, and the pressurizing device is controlled by the pressurizing-device control device on the basis of the detected output pressure of the pressurizing device, so as to reduce the influence of the fluid flows through the pressure control valve device.
For the pressure sensor to be able to detect with high efficiency and accuracy a change of the output pressure of the pressurizing device due to the switching operation of the pressure control valve devices, the pressure sensor is preferably disposed at a position as close as possible to the pressure control valve devices, namely, in a fluid passage connecting the pressurizing device and the pressure control valve devices, desirably in a portion of the fluid passage near the pressure control valve devices. However, the pressurizing device may incorporate the pressure sensor. Alternatively, each pressure control valve device may incorporate the pressure sensor.
(6) A braking pressure control apparatus according to the above mode (5), wherein said pressurizing device includes (a) a pump device operable to pressurize the working fluid, and (b) a master cylinder including a cylinder housing, and a pressurizing piston which is fluid-tightly and slidably fitted in the cylinder housing and which cooperates with the cylinder housing to define a rear pressurizing chamber) connected to the pump device and a front pressurizing chamber connected to the corresponding at least one brake cylinder, the pressurizing piston being advanced by an increase in the pressure of the pressurized fluid which is supplied from the pump device into the rear pressurizing chamber, so that the pressure in the front pressurizing chamber is increased,
and wherein the pressure sensor includes at least one of a sensor for detecting the pressure of the fluid in the front pressurizing chamber, and a sensor for detecting the pressure of the fluid in the rear pressurizing chamber.
(7) A braking pressure control apparatus according to any one of the above modes (1)-(6), wherein the pressurizing-device control device includes a pressure increase control portion operable to increase the output pressure of the pressurizing device when an amount of the fluid to be supplied into the at least one brake cylinder corresponding to each of the pressure control valve devices tends to be increased by each pressure control valve device, and a pressure reduction control portion operable to reduce the output pressure of the pressurizing device when an amount of the fluid to be discharged from the at least one brake cylinder corresponding to each pressure control valve device tends to be increased by each pressure control valve device.
In the braking pressure control apparatus according to the above mode (7), the output pressure of the pressurizing device is increased when each pressure control valve device is placed in a state for increasing the amount of the fluid to be supplied into the corresponding at least one brake cylinder. Accordingly, an undesirable reduction of the output pressure due to the fluid supply from the pressurizing device into the corresponding at least one brake cylinder can be reduced. Each pressure control valve device may include a simple solenoid-operated shut-off valve disposed between the pressurizing device and the corresponding at least one brake cylinder, or a flow control valve whose opening is variable with a change in an amount of electric current to be applied thereto, to control a rate of flow of the fluid between the pressurizing device and the corresponding at least one brake cylinder. Where the pressure control valve device includes the solenoid-operated shut-off valve, the amount of the fluid to be supplied to the corresponding at least one brake cylinder can be increased by holding the shut-off valve in the open state, or by alternately placing the shut-off valve in the open and closed state with a controlled duty ratio or cycle, as described above with respect to the above mode (4).
When the pressure control valve device is placed in a state for increasing the amount of the fluid to be discharged from the brake cylinder, the output pressure of the pressurizing device is reduced, so that an undesirable increase of the output pressure due to the discharge from the brake cylinder toward the pressuring device can be reduced.
(8) A braking pressure control apparatus according to any one of the above modes (1)-(7), wherein the pressurizing-device control device includes a first control portion operable to control the output pressure of the pressurizing device on the basis of a condition of an automotive vehicle on which the braking system is provided, and a second control portion operable to control the output pressure on the basis of the operating state of the pressure control valve device.
In the braking pressure control apparatus according to the above mode (8), the first control portion controls the output pressure of the pressurizing device on the basis of the condition of the vehicle. When a brake operating member for activating the braking system is in operation, for example, the output pressure is controlled by the first control portion on the basis of the amount of operation of the brake operating member. When the brake operating member is not in operation, the output pressure is controlled on the basis of the running condition of the vehicle, such as the slipping state of a slipping drive wheel or wheels, a condition of turning of the vehicle, a running speed of the vehicle, and an acceleration value of the vehicle wheels. The control of the output pressure of the pressurizing device on the basis of the vehicle running condition includes not only a control in which the output pressure is controlled to a value corresponding to the vehicle running condition, but also a control in which the output pressure is controlled to a predetermined value, as in the traction control, vehicle running stability control, and vehicle turning stability control. The predetermined value indicated above may be the same in all of the different controls indicated above, or may be different in the respective different controls. Alternatively, the value to which the output pressure is controlled may be determined on the basis oaf the vehicle running condition at the time the traction control or other appropriate control is initiated. The control of the output pressure on the basis of the vehicle running condition also includes an automatic braking control in which the output pressure is controlled to a value corresponding to the vehicle running condition that requires an automatic brake application to the vehicle. For example, the automatic braking control is effected when a distance between the vehicle in question and an object in front of the vehicle (a vehicle running in front of the vehicle) becomes smaller than a predetermined threshold. In this case, the output pressure is controlled to a value which is determined by the distance between the vehicle and the object, a rate of change of the distance, or a derivative of the rate of change.
On the other hand, the second control portion controls the output pressure of the pressurizing device on the basis of the operating state of each pressure control valve device. For instance, the second control portion controls the output pressure such that the output pressure is higher when the pressure control valve device is placed in a fluid-supply state for supplying the pressurizing fluid from the pressurizing device into the brake cylinder, than when the pressure control valve device is placed in a closed state for inhibiting the fluid supply into the brake cylinder. Alternatively, the second control portion controls the output pressure such that the output pressure is higher within a predetermined period of time after the pressure control valve device is switched from the closed state to the fluid-supply state, than after the predetermined period of time has expired. Similarly, the second control portion controls the output pressure such that the output pressure is lower when the pressure control valve device is placed in a fluid-discharge state for discharging the fluid from the brake cylinder to the pressurizing device, than when the pressure control valve device is placed in a closed state for inhibiting the fluid discharge from the brake cylinder to the pressurizing device. Alternatively, the second control portion controls the output pressure such that the output pressure is lower within a predetermined period of time after the pressure control valve device is switched from the closed state to the fluid-discharge state, than after the predetermined period of time has expired.
The output pressure of the pressurizing device may be controlled to a value different from the value determined by the first control portion, for instance, to a value which is larger or smaller by a suitable adjusting amount, than the value determined by the first control portion. The adjusting amount may be a predetermined value, or a value which changes with the running condition of the vehicle or a difference between the present output pressure of the pressurizing device and the fluid pressure in the brake cylinder. Where the pressure control valve device is controlled on the basis of the vehicle running condition, the operating state of the pressure control valve device or the state of fluid flow through the pressure control valve device can be determined on the basis of the vehicle running condition. In this respect, it is reasonable to determine the adjusting amount of the basis of the vehicle running condition.
The second control portion controls the output pressure of the pressurizing device to a value different from that determined by the first control portion, for instance, to one of a minimum value, a maximum value and an intermediate value which is selected depending upon the operating state of the pressure control valve device. Those minimum, maximum and intermediate values are determined by the capacity of the pressurizing device. Alternatively, the output pressure is controlled according to a predetermined pattern, or on the basis of the vehicle running condition or the difference between the output pressure of the pressuring device and the pressure of the brake cylinder.
The second control portion may be considered to be a portion for adjusting or changing the output pressure of the pressurizing device which has been determined by the first control portion.
(9) A braking pressure control apparatus according to any one of the above modes (1)-(8), wherein the pressurizing device includes a pressurizing portion for pressurizing the working fluid, and a pressure-reducing control valve capable of controlling the output pressure of the pressurizing device by reducing the pressure of the fluid pressurized by the pressurizing portion,
and wherein the pressurizing-device control device includes a pressure-reducing-valve control portion operable to control the pressure-reducing control valve on the basis of the state of flow of the fluid between the pressurizing device and the corresponding at least one brake cylinder.
The influence of the fluid flow to and from the brake cylinder on the output pressure of the pressurizing device can be reduced by controlling the pressure-reducing control valve on the basis of the state of flow of the fluid between the pressurizing device and the brake cylinder.
The pressure-reducing control valve of the pressurizing device may be a solenoid-operated shut-off valve which is alternately opened and closed with a controlled duty ratio or cycle, or a linear pressure-reducing control valve the opening of which is controllable by controlling the electric current applied thereto.
(10) A braking pressure control apparatus according to the above mode (9), wherein the pressure-reducing control valve is a solenoid-operated linear control valve capable of controlling the pressure of the fluid pressurized by the pressurizing portion to a value corresponding to an amount of electric current applied thereto,
and wherein the pressure-reducing-valve control portion includes an electric current control portion for controlling the electric current to be applied to the solenoid-operated linear control valve.
In the apparatus according to the above mode (9), the output pressure of the pressurizing device can be efficiently controlled by controlling the amount of electric current to be applied to the linear control valve, which will be described in detail in the DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.
(11) A braking pressure control apparatus according to any one of the above modes (1)-(10), wherein the pressurizing device comprises a pump device including a pump for pressuring the working fluid, and a pump drive source for driving the pump, and the pressurizing-device control device includes a pressurizing-capacity control portion operable to control a pressurizing capacity of the pump device on the basis of the operating state of each pressure control valve device which determines the state of flow of the fluid between the pressurizing device and the corresponding at least one brake cylinder.
The undesirable reduction and increase of the output pressure of the pressurizing device due to the fluid flow to and from the wheel brake cylinder can be reduced by increasing and reducing the pressurizing capacity of the pump device, respectively.
(12) A braking pressure control apparatus according to the above mode (11), wherein the pump drive source is an electric motor, and the pressurizing-capacity control portion includes a speed control portion operable for controlling an operating speed of the electric motor.
The operating speed of the electric motor can be controlled by controlling an amount of electric energy supplied to the electric motor, so that the pressurizing capacity of the pump device can be controlled.
The delivery pressure and rate of the fluid pressurized by the pressurizing device are determined by the fluid pressure in the brake cylinder to which the pressurized fluid is supplied, so that the delivery pressure and rate are not necessarily increased by increasing the operating speed of the electric motor. However, the pressurizing capacity of the pump device can be increased by controlling the amount of electric energy to be supplied to the electric motor, so as to increase the operating speed of the electric motor.
(13) A braking pressure control apparatus according to any one of the above modes (1)-(12), wherein the pressurizing-device control device controls the pressurizing device according to a highest one of desired values of the fluid pressures in the plurality of brake cylinders.
By controlling the pressurizing device according to a highest one of the desired fluid pressures in the plurality of brake cylinders, it is possible to avoid insufficiency of the fluid pressure in each of the plurality of brake cylinders which are activated for a given purpose, and also possible to prevent the fluid pressures in the brake cylinders from rising to an excessively high level as compared with the desired values when the pressurized fluid is supplied from the pressurizing device to the brake cylinders. The pressurizing device according to the above mode (13 makes it possible to reduce the required frequency of operations of the pressure control valve device to control the fluid pressure in the corresponding at least one brake cylinder.
Where each of the plurality of brake cylinders is controlled such that the actual fluid pressure coincides with the desired braking pressure determined for that brake cylinder, the output pressure of the pressurizing device is controlled according to a highest one of the desired braking pressures of the brake cylinders, more specifically, such that the output pressure is controlled to be equal to the highest desired braking pressure or equal to a value corresponding to the highest desired braking pressure. The actual fluid pressures in the brake cylinders are controlled to be equal to the determined desired braking pressures, in the front-rear braking-force distribution control, left-right braking-force distribution control, braking effect control, automatic braking control, vehicle turning stability control and vehicle running stability control, which will be described in detail in the DESCRIPTION OF THE PREFERRED EMBODIMENTS.
Where the fluid pressure in the brake cylinder for a slipping drive wheel is controlled for the traction control of an automotive vehicle so that the slipping amount of the slipping wheel is held within an optimum range, one of the wheel brake cylinders whose fluid pressure tends to be insufficient is determined on the basis of the operating states of the pressure control valve devices corresponding to the brake cylinders, and the output pressure of the pressurizing device is controlled so that the slipping amount of the wheel corresponding to the wheel brake cylinder whose fluid pressure tends to be insufficient is held within the optimum range, as described in derail in the DESCRIPTION OF THE PREFERRED EMBODIMENTS. By controlling the output pressure of the pressurizing device in the manner described above, the output pressure is eventually controlled according to the highest one of the desired braking pressures of the plurality of wheel brake cylinders.
Where the pressurizing device includes at least one of the pressure-reducing control valve and the pump device which have been described, the output pressure of the pressurizing device may be controlled by controlling the pressure-reducing control valve or the pump device.
(14) A braking pressure control apparatus according to any one of the above modes (1)-(13), further comprising a valve-device control portion operable to control each of the pressure control valve devices for regulating the fluid pressure in said corresponding at least one brake cylinder, and wherein the pressurizing-device control device includes a constant-pressure control portion operable to control the pressurizing device such that the output pressure is held at a predetermined constant value.
In the apparatus according to the above mode (14), the pressurizing device is controlled such that the output pressure is held at a predetermined constant value, and the fluid pressure in each brake cylinder is controlled by the corresponding brake control valve device. The predetermined constant value may be the same in all of the different controls (such as the traction control), may be different in the respective different controls, or may be determined on the basis of the vehicle running condition at the time the traction control or other appropriate control is initiated.
(15) A braking pressure control apparatus for a braking system having a plurality of brake cylinders, said braking pressure control apparatus comprising:
a pressurizing device capable of pressurizing a working fluid and controlling a pressure of the pressurized fluid:
a plurality of pressure control valve device each of which is disposed between the pressurizing device and at least one of the plurality brake cylinders and is operable to control flows of the fluid between the pressurizing device and the corresponding at least one brake cylinder, for thereby regulating the fluid pressure in the corresponding at least one brake cylinder; and
a pressurizing-device control device for controlling the pressurizing device to control an output pressure of the pressurizing device, the pressurizing-device control device including a forecasting type control portion operable to initiate an operation of controlling the output pressure of the pressurizing device upon detection of a symptom indicating that the pressure control valve device will be operated within a predetermined time to initiate a flow of the fluid between the pressuring device and the corresponding at least one brake cylinder.
In the braking pressure control apparatus constructed according to the above mode (15) of this invention, the control of the output pressure of the pressurizing device is initiated upon detection of a symptom indicating that the pressure control valve device will be operated within a predetermined time, namely, in the near future, to initiate a flow of the fluid between the pressurizing device and the corresponding at least one brake cylinder. Accordingly, an undesirable influence of the fluid flow to and from the brake cylinder or cylinder on the output pressure of the pressurizing device can be efficiently reduced.
In the present apparatus, the forecasting type control portion of the pressurizing-device control device is adapted to initiate the control of the output pressure of the pressurizing device when an operation of each pressure control valve device to initiate a fluid flow between the pressurizing device and the at least one brake cylinder is expected to take place in the near future, that is, upon detection of a symptom indicating that such a fluid flow will highly probably take place in a short time. Even if this symptom is detected (and the operation to control the pressurizing device is initiated by the forecasting type control portion), the fluid flow may not in fact take place. In this case, however, there does not arise a problem since the operation to control the pressurizing device does not cause a considerable amount of change of the output pressure of the pressurizing device.
The braking pressure control apparatus according to the above mode (15) may include a technical feature according to any one of the above modes (1)-(14).
(16) said forecasting type control portion includes a running-condition forecasting portion operable on the basis of a running condition of an automotive vehicle on which the braking system is provided, to forecast whether a switching operation of each pressure control valve device will take place to initiate the flow of the fluid between the pressurizing device and the corresponding at least one brake cylinder.
Where each pressure control valve device is controlled by a valve-device control device depending upon the running condition of the vehicle, a symptom indicating that a fluid flow will take place between the pressurizing device and the corresponding at least one brake cylinder can be detected on the basis of the running condition of the vehicle.
For instance, the pressurized fluid is supplied to the at least one brake cylinder through the pressure control valve device when the stability of the running condition of the vehicle is reduced below a predetermined lower limit. In this case, it is determined that there exists the symptom indicating that the fluid flow will take place in the near future, if the stability of the vehicle running condition is reduced below a predetermined threshold higher than the above-indicated lower limit and if the stability is being deteriorated.
(17) A braking pressure control apparatus according to any one of the above modes (1)-(16), wherein the pressurizing device includes:
a pump device operable to pressurize the working fluid; and
a master cylinder including a cylinder housing, and a pressurizing piston which is fluid-tightly and slidably fitted in the cylinder housing and which cooperates with the cylinder housing to define a rear pressurizing chamber connected to the pump device and a front pressurizing chamber connected to the corresponding at least one brake cylinder, the pressurizing piston being advanced by an increase in the pressure of the pressurized fluid which is supplied from the pump device into the rear pressurizing chamber, so that the pressure in the front pressurizing chamber is increased.
The braking pressure control apparatus according to the above mode (17) uses one preferred form of the pressurizing device. This apparatus will be described in detail in the DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.
(18) A braking pressure control apparatus for a braking system having a plurality of brake cylinders, the braking pressure control apparatus comprising:
a pressurizing device including a pump device operable to pressurize a working fluid, and a master cylinder having a cylinder housing, and a pressurizing piston which is fluid-tightly and slidably fitted in the cylinder housing and which cooperates with the cylinder housing to define a rear pressurizing chamber connected to the pump device and a front pressurizing chamber connected to the corresponding at least one brake cylinder, the pressurizing piston being advanced by an increase in the pressure of the pressurized fluid which is supplied from the pump device into the rear pressurizing chamber, so that the pressure in the front pressurizing chamber is increased;
a plurality of pressure control valve devices each of which is disposed between the pressurizing device and at least one of the plurality of brake cylinders and is operable to control flows of said fluid between the pressurizing deice and the corresponding at least one brake cylinder, for thereby regulating the fluid pressure in the corresponding at least one brake cylinder, for thereby regulating the fluid pressure in the corresponding at least one brake cylinder; and
a control device operable to control at least one of the pressurizing device and each pressure control valve device, for thereby regulating the fluid pressure in the corresponding at least one brake cylinder.
The control device provided in the braking pressure control apparatus according to the above mode (18) is operable in one of the following three modes:
1) The control device controls each pressure control valve device while the output pressure of the pressurizing is held at a predetermined substantially constant value.
In the above mode of operation, the predetermined value of the output pressure of the pressurizing device is preferably determined so as to avoid insufficiency of the fluid pressure in all of the at least one brake cylinder corresponding to each pressure control valve device. Each pressure control valve device may include a solenoid-operated shut-off valve which is opened and closed as needed or a solenoid-operated control valve capable of controlling the fluid pressure in the corresponding at least one brake cylinder according to an amount of electric current to be applied to that valve. The solenoid-operated shut-off valve may be alternately opened and closed with a controlled duty ratio or cycle.
The pressurizing device may be controlled to be held in a substantially constant operating state. In this case, the output pressure of the pressurizing device may be more or less varied due to fluid flows between the pressurizing device and the at least one brake cylinder through the pressure control valve device, but can be held at a substantially constant value.
2) The control device controls the output pressure of the pressurizing device according to a highest one of desired values of the fluid pressures in the brake cylinders, and controls the pressure control valve device corresponding to the brake cylinder whose desired fluid pressure value is the highest, such that this brake cylinder is held in communication with the pressurizing device through the corresponding pressure control valve device, while controlling the other pressure control valve device or devices so as to regulate the fluid pressure or pressures in the corresponding brake cylinder or cylinders.
Where the output pressure of the pressurizing device is controlled to be equal to the highest one of the desired fluid pressures of the brake cylinders, the fluid pressure in the brake cylinder whose desired fluid pressure is the highest is made equal to the output pressure of the pressurizing device, by holding that brake cylinder in communication with the pressurizing device. Thus, the fluid pressure of this brake cylinder can be controlled to be equal to the desired value. The fluid pressures in the other brake cylinders are controlled by controlling the corresponding pressure control valve device or devices.
Where the output pressure of the pressurizing device is controlled to be proportional to the highest one of the desired fluid pressure values of the brake cylinders, the fluid pressure in the brake cylinder whose desired fluid pressure is the highest must also be controlled as needed by the corresponding pressure control valve device.
In either of the two cases indicated above, the pressure of the pressurized fluid to be supplied from the pressurizing device to the brake cylinders will not be excessively high or low.
The above-indicated two modes of operation of the control device are suitable where the fluid pressures in the individual brake cylinders are controlled to respective different desired values independently of each other.
3) The control device controls the pressurizing device such that the output pressure of the pressurizing device is equal to the desired pressure of the brake cylinder or cylinders, and controls the pressure control valve devices such that the pressurizing device is held in communication with the brake cylinder or cylinders through the pressure control valve device or devices.
This mode of operation is suitable where the fluid pressures in the two or more brake cylinders are controlled to the same desired value. The desired fluid pressure can be established in all of the brake cylinders by controlling the output pressure of the pressuring device to be equal to the desired fluid pressure of the brake cylinders and holding the brake cylinders in communication with the pressurizing device. This control arrangement eliminates a need of controlling the pressure control valve devices for controlling the corresponding brake cylinders, or reduces the required number of operations of the pressure control valve devices, resulting in reduced operating noise and vibration of the pressure control valve devices.
The braking pressure control apparatus according to the above mode (18) may incorporate any technical feature according to any one of the above modes (1)-(17).
(19) A braking pressure control apparatus according to the above mode (18), wherein the pressurizing device further includes a pressure-reducing control valve capable of controlling the pressure of the fluid pressurized by the pump device, and wherein the control device activates the pump device prior to an operation of each pressure control valve device is initiated to regulate the fluid pressure in the corresponding at least one brake cylinder, the control device controlling the pressure-reducing control valve such that the output pressure of the pressurizing device after activation of the pump device does not exceed a value before activation of the pump device.
Where there is a high probability that an operation of the pressure control device to regulate the fluid pressure in the corresponding at least one brake cylinder will be performed in the near future, that is, within a predetermined relatively short time, a delay in regulating the brake cylinder pressure can be reduced by activating the pump device prior to that operation of the pressure control valve device. Further, the pressure control valve device is controlled so as to prevent the output pressure of the pressurizing device after the activation of the pump device from exceeding the value before the activation of the pump device. This control arrangement makes it possible to avoid an unnecessary increase of the brake cylinder pressure, without having to control the corresponding pressure control valve device.
The braking pressure control apparatus according to the above mode (19) is suitable where the fluid pressures in the brake cylinders are controlled while a brake operating member for activating the braking system is not in operation, in particular, where the traction control, vehicle running stability control, vehicle turning stability control and automatic braking control are effected. In these controls, the fluid pressure in each brake cylinder under control is initially increased in most cases, and an increase of the brake cylinder pressure may be delayed if the pressurized fluid is not rapidly supplied from the pressurizing device to the brake cylinder. This control delay is increased with a decrease in the ambient temperature and with a consequent increase in the viscosity of the working fluid. Where the traction control is initiated on a road surface having a relatively high friction coefficient, the desired rate of increase of the brake cylinder pressure is relatively large (the brake cylinder pressure is required to be increased at a relatively high rate) immediately after the traction control is initiated. In this case, therefore, the control delay due to the low rate of supply of the pressurized fluid to the brake cylinder may be serious. In the present apparatus, however, the pump device is activated prior to the initiation of the traction control, so that the pressurized fluid can be supplied from the pressurizing device to the brake cylinder at a sufficiently high rate, making it possible to minimize the control delay.
(20) A braking control apparatus for a braking system having a plurality of brake cylinders, said braking control apparatus comprising:
a pressurizing device capable of pressurizing a working fluid and controlling a pressure of the pressurized fluid to a desired basic value;
a plurality of pressure control devices which are disposed between the pressurizing device and the plurality of brake cylinders, respectively and each of which is operable to control flows of the fluid between the pressurizing device and a corresponding one of the brake cylinders, for thereby regulating the fluid pressure in the corresponding brake cylinder; and
a pressurizing-device control device including at least one of a pressure-increase control portion and a pressure-reduction control portion, the pressure-increase control portion being operable to control the pressurizing device such that an output pressure of the pressurizing device is controlled to a value higher than the desired basic value when at least one of the plurality of pressure control valve devices is operated to supply the pressurized fluid to the corresponding brake cylinder, the pressure-reduction control portion being operable to control the pressurizing device such that the output pressure is controlled to a value lower than the desired basic value when at least one of the plurality of pressure control valve devices is operated to discharge the pressurized fluid from the corresponding brake cylinder.
In the braking pressure control apparatus according to the above mode (20), the pressurizing-device control device may further includes a third control portion than said pressure-increase control portion and/or said pressure-reduction control portion, which are operated depending upon the state of flow of the fluid between the pressurizing device and the pressure control valve device. This third control portion is operable to control the pressuring device such that the output pressure is controlled to be equal to the desired basic value.
The braking pressure control apparatus according to the above mode (20) may incorporate any technical feature according to any one of the above modes (1)-(19).